1. Field of Invention
The present invention relates to a drawing machine.
2. Related Prior Art
Referring to FIGS. 9 and 10, there is shown a conventional drawing machine 1 including a clamping device and a driving device. The clamping device includes a lower plate, two rails, two slides, two jaws 3, two rods, an upper plate, a transmit element and a cylinder 4. The rails extend on the top of the lower plate and get closer to each other from a first end to a second end. The slides are movable along the rails. The jaws 3 are carried on the slides. The rods are raised from the slides. The upper plate is attached to the lower plate. The transmit element is movable on the upper plate and connected to the rods inserted through the upper plate. The cylinder 4 is a pneumatic or hydraulic cylinder for moving the transmit element on the upper plate. The cylinder 4 can move the transmit element. The transmit element can move the rods. The rods move the slides. The slides move the jaws 3. The jaws 3 get closer to each other for clamping a bar or pipe to be drawn. The driving device includes two following rollers and a driving element 2. The following rollers are attached to the second surface of the lower plate. The driving element 2 includes a shaft and a ridge extending on the shaft and acting as a cam. The ridge is engaged with the following rollers. As the shaft is rotated, the following rollers are moved by the ridge so that the clamping device is moved. Thus, the bar or pipe is drawn. However, the conventional drawing machine is not reliable for several reasons. Firstly, it is difficult to keep the pressure of the fluid in the cylinder 4 at an intended value. Secondly, there is drag in the transmission of the fluid in the cylinder 4 and a related piping. A related circuit for controlling the cylinder 4 is vulnerable to malfunctioning.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in the prior art.